From: Chuck Lever Date: Tue, 7 May 2024 13:37:14 +0000 (-0400) Subject: NFSD: Force all NFSv4.2 COPY requests to be synchronous X-Git-Tag: io_uring-6.10-20240523~40^2 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=8d915bbf39266bb66082c1e4980e123883f19830;p=linux-2.6-block.git NFSD: Force all NFSv4.2 COPY requests to be synchronous We've discovered that delivering a CB_OFFLOAD operation can be unreliable in some pretty unremarkable situations. Examples include: - The server dropped the connection because it lost a forechannel NFSv4 request and wishes to force the client to retransmit - The GSS sequence number window under-flowed - A network partition occurred When that happens, all pending callback operations, including CB_OFFLOAD, are lost. NFSD does not retransmit them. Moreover, the Linux NFS client does not yet support sending an OFFLOAD_STATUS operation to probe whether an asynchronous COPY operation has finished. Thus, on Linux NFS clients, when a CB_OFFLOAD is lost, asynchronous COPY can hang until manually interrupted. I've tried a couple of remedies, but so far the side-effects are worse than the disease and they have had to be reverted. So temporarily force COPY operations to be synchronous so that the use of CB_OFFLOAD is avoided entirely. This is a fix that can easily be backported to LTS kernels. I am working on client patches that introduce an implementation of OFFLOAD_STATUS. Note that NFSD arbitrarily limits the size of a copy_file_range to 4MB to avoid indefinitely blocking an nfsd thread. A short COPY result is returned in that case, and the client can present a fresh COPY request for the remainder. Signed-off-by: Chuck Lever --- diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c index ea3cc3e870a7..46bd20fe5c0f 100644 --- a/fs/nfsd/nfs4proc.c +++ b/fs/nfsd/nfs4proc.c @@ -1807,6 +1807,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, __be32 status; struct nfsd4_copy *async_copy = NULL; + /* + * Currently, async COPY is not reliable. Force all COPY + * requests to be synchronous to avoid client application + * hangs waiting for COPY completion. + */ + nfsd4_copy_set_sync(copy, true); + copy->cp_clp = cstate->clp; if (nfsd4_ssc_is_inter(copy)) { trace_nfsd_copy_inter(copy);